Investigation of effect of slot opening on fractional slot and integer slot axial flux permanent magnet machine

This research attempts to compare the effects of the slot opening on axial flux permanent magnet machines with the fractional slot concentrated winding and the integer slot toroid winding. Analytical derivations of winding function, flux linkage, and back-EMF are presented, paying special attention to the slot opening. Specific machines having 24 slots 28 poles, 24 slots 20 poles, and 84 slots 28 poles are compared. Comparison results shows that the slot opening contributes to reducing the harmonics of the back-EMF in the axial flux permanent magnet machines having fractional slot concentrated winding, while it increases harmonics of the back-EMF in the axial flux permanent magnet machines having integer slot toroid winding. Slot opening ratio considerably varies total harmonic distortion of back-EMF in axial flux permanent magnet machine with fractional slot concentrated winding while it has negligible effect on the harmonic distortion of axial flux permanent magnet machine with integer slot toroid winding.